This invention relates to a method and apparatus for treating soil, sludge and the like, in situ, and more particularly to a process and apparatus for introducing additives to soil, sludge and the like, to neutralize or remediate contamination and/or to solidify and/or stabilize soil.
Heretofore a significant number of petroleum refineries in the United States and other industrialized countries have generated asphaltic waste material with very high concentrations of sulfuric acid and sulfur dioxide. Usually, these materials were merely dumped into natural depressions in the surrounding terrain and impounded there by earthen berms. A number of sites have accumulations of well over 100,000 tons of such materials. The content of these impoundments are lethal to life in general and in many cases have begun to affect the ground water on adjacent properties. Owners of such sites have attempted to eliminate the liability associated therewith by neutralizing or otherwise disposing of the asphaltic waste material.
Because of the sulfur dioxide and the sulfuric acid contained in lagoons and solidified or partially solidified asphaltic sludge dumping sites, such sites cannot be excavated in a normal manner, because of the potential for release of a lethal concentration of sulfur dioxide gas. The most sensible and economical approach to eliminating the potential liability associated with such waste sites is to neutralize the high concentration of sulfuric acid and absorb the sulfur dioxide gas with common neutralizers containing calcium, magnesium or sodium, preferably in situ. In many cases the neutralized sludge is deemed non-hazardous and is left in the original lagoons, but in other cases, the neutralized material must be excavated and impounded in a certified landfill. In either case, the neutralizer must be applied as the material is excavated or otherwise disturbed. Several devices have used rotary cutters of different types to bore or cut into the sludge while pumping in a lime slurry. These devices are usually mounted on cranes, large hydraulic excavators or other mobile platforms, and sometimes incorporate fume collecting hoods. In some cases, contractors merely spread a few inches of lime on the surface of the sludge, which much of the time is hard enough to support heavy equipment, grind the lime into the sludge at about 1 foot depth at a time, and then remove the pulverized material, except for a few inches which is left as a barrier to prevent gas from escaping from the surface.
The above processes have several major drawbacks. The rotary boring equipment which plunges axially while injecting lime slurry is 20% inefficient geometrically because overlapping is needed to treat all of the material between the columns. Such rotary boring equipment must also use a lime slurry so that it can be pumped to the cutter head, thus entailing the steps of slurrying and pumping. Rotary cutting equipment that enters the sludge at a right angle to its axis must also use lime slurry if it is plunged to significant depths, and at greater depths it is difficult to control the actual position of the cutter head which leads to more under or over treatment. Rotary equipment that is used to treat lagoons layer by layer does not need a slurry and can use dry or damp neutralizers or even by-product limes which are less expensive. But, such equipment is only appropriate where the sludges will be removed to adjacent landfills. To remove a 20 foot thickness of sludge, approximately 20 applications of neutralizer and 20 passes with the rotary cutter will be used between 20 operations to haul the treated material out of the lagoon.
U.S. Pat. No. 5,242,246, discloses a surface remediator which includes a conventional trenching machine provided with elongated crawler tracks or treads. A vertically adjustable boom is also provided with either a single or pair of endless drive chains mounted on opposite sides thereof.
Also mounted on the trenching machine is a process conveyor which receives soil to be processed or treated, and which is arranged for immediately returning and replacing soil in the trench behind the trenching machine. A backfill shield having a generally U-shaped cross-section is mounted in close proximity to the trailing end of the boom. The patent discloses the processing of contaminated soil, and includes a rock crusher and a vibrating screen table which can be used to separate large rocks before the soil is discharged into the crusher. The process conveyor includes a heated section and a treatment section located down stream of the heated section. The heated section is designed to liberate volatile contaminates from the soil, which are injected into a gas outlet conduit where the gases are scrubbed in a scrubber before being discharged into the atmosphere. A contaminate residue tank collects harmful contaminants removed by the scrubber. In the treatment section, wet and dry reagents are combined with the contaminated soil from a plurality of feedlines. The neutralized soil is discharged into a chute on the opposite side of the boom. A backfield shield prevents the process soil from coming into contact with the contaminated soil. The patent does not however disclose a method and apparatus for treating soil, sludge, and other material in situ, but to the contrary teaches an apparatus and method wherein soil is removed from the ground, processed on board a mobile apparatus, and returned to the ground. Accordingly, the apparatus is relatively complex, and despite the use of shields, presents a considerable risk that gases, possibly lethal levels, will escape into the atmosphere.
U.S. Pat. No. 5,118,230 discloses a method and apparatus for installing a leachate contaminant system, wherein an impermeable liner is deployed simultaneously with a trenching operation. A trenching tool includes a pivotal mounted boom, and a plurality of digging tools mounted on a chain. Extending into the soil retainment device is a slotted feed tube, into which is fed, from a supply reel, a liner carrier case. As the impermeable barrier is carried from the liner carrier case, a continuous length of impermeable barrier is formed. The leachate contaminant system is used to surround a contaminated site, such as a landfill or a hazardous dump site. The patent therefore does not provide an in situ treatment method but instead provides a method of providing a containment around an existing site.
In view of the known technology for controlling or eliminating hazardous waste sites, there remains a need for an apparatus and method for safely and economically treating soil, sludge and the like in situ.